Commentary: The new frontier of intracardiac mapping.

Carl L. Backer, MD

The Boston Children's group has developed a mapping catheter that can be used intraoperatively to identify the location of the conduction system to decrease the incidence of heart block requiring permanent postoperative pacing.

See Article page 159.

The pediatric cardiac surgical and electrophysiology teams from Boston Children's Hospital have developed a novel mapping catheter that can be used intraoperatively to identify the location of the conduction system of the heart. This revolutionary tool will reduce the incidence of postoperative heart block requiring permanent pacing. This is certainly among the holy grails for congenital heart surgeons: Having the ability during an operation to know where the conduction system is and avoid it—even in the most complex cases.

The high-risk population the authors have targeted for this intervention has complex intracardiac anatomy that requires extensive septal and outflow tract surgery to achieve a biventricular circulation. Many of these patients would have been previously considered Fontan candidates.

The authors describe their use of intraoperative conduction mapping for complex biventricular conversion in 2 patients. The mapping was used to identify safe areas to enlarge ventricular septal defects and avoid the conduction system. Interestingly, in 1 patient the conduction tissue was found to be located where expected. In the second patient, the conduction system was located in a totally unexpected area. They note that in their overall experience the conduction system was in an unexpected location in fully 20% of their cases.

I am certain that congenital heart surgeons are hopeful that this technology can be steadily improved to the point where it could potentially be used in even more straightforward cases. That being said, the fact that the procedure requires a careful decompression of the heart and mapping with the heart beating inserts the risk of air embolism to the procedure. This inherent risk of the current technology will probably limit its use to these more complex patients with heterotaxy, unbalanced atrioventricular septal defect, double-outlet right ventricle, and complex transposition of the great arteries. The mapping still requires the heart to be actively beating to obtain the electrogram. The catheter size and rigidity also pose some constraints in terms of accessing certain areas of the heart.

Finally, current histopathologic studies with advanced technology continue to solidify our understanding of the location of the conduction system in patients undergoing repair of standard defects with normal situs and standard ventricular looping.

I congratulate the Boston Children's surgery and electrophysiology teams for this substantial advance in our ability to map the conduction system and look forward to further evolution of their mapping catheter techniques. I am confident they will continue to miniaturize the catheters and standardize the techniques to make this a more routine part of complex reconstruction.